You really captured the sense of hustle-and-bustle of being in a transport station. I've never been to St. Pancras International but the closest thing I can think of that I've had experience with is O'Hare airport in Chicago. To me there's almost a sense of urgency; I can see people hurrying and trying to make their plane/bus/train with their suitcases while moving through a crowd of people.
The vast production, in my opinion, also shows a feeling of determination. The imagery I get is something like: You're at the bottom of a large cliff, there's nowhere to go but up, and come Hell or high water you're going to climb it.
I'm not quite sure if that's what you were going for, but that's how I see it.
Reading your description it seems like one thing you were going for, though, was a sense of optimism and freedom. I can definitely see that.
The only thing that keeps this from getting 5 stars from me is this: To me, something about the flow of the piece seems to get in the way of what you're trying to do. I think this is especially the case when the quiet part hits towards the middle. I'm wondering if it would be more effective if there was a continuous buildup of instrumentation to reflect ever-growing positive energy, and at the end is where the quiet part would come in. Just something you may want to play around with.
Overall, I'd say you did a phenomenal job. :)
More info about how I review music here: https://codefreq.newgrounds.com/news/post/1089806